On Mon, Jan 15, 2018 at 11:15 PM, Luke Dashjr <luke@dashjr.org> wrote:

On Tuesday 16 January 2018 1:06:14 AM Rusty Russell via bitcoin-dev wrote:
> The rule AFAICT is "standard transactions must still work". This was
> violated with low-S, but the transformation was arguably trivial.
>
> OTOH, use of altstack is completely standard, though in practice it's
> unused and so only a theoretical concern.

I'm not aware of a single standard/BIP that uses the altstack at all.

By "standard transaction" here, Rusty means that (P2SH or Segwit) scripts that use the alt-stack pass the standardness checks and will be relayed by recent Bitcoin Core software.

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Regarding lowS: I think the more severe standardness change was the added requirement that (some of the) pubkeys in a multisig must be parsable. I have talked with people who cannot retrieve their funds now, when before they could. However, like lowS, this was only a change to the standardness rules and not a consensus change, so these funds are not necessarily permanently lost. They can be retrieved with miner help.

I don't see how BIP 117, which is a change in consensus rules that could cause permanent loss of otherwise well-secured funds (in addition to the other issues raised about BIP 117), is even comparable to the previous changes in only the standardness rules.